甘肃黑河中下游影响绿洲植被发育的某些因素

Some factors affecting the development of vegetations in the middle and lower reaches of the Heihe River, Gansu, China.

黑河下游额济纳绿洲区和中下游沿黑河干流河床附近的潜水位埋深较浅,是维系地表植被生长的重要因素。中游高台附近潜水位存在每年双峰值的变化,较之下游额济纳绿洲潜水位每年单峰值的变化更有利于植被的生长。在包气带剖面中,同一时刻水土势、含水量、含盐量随深度的变化趋势基本相同。采样点包气带土壤中易溶离子含量相对较低,全盐量小于5%,中游采样点土壤中以HCO3-为主,下游以SO42-为主,由SO42-、Cl-和Na+、Ca2+组成的盐类构成了包气带土壤中的主要盐分。土壤中易溶离子含量自地表至潜水面之间随深度总体上呈减小趋势。植被的根系分布对包气带土壤含水量、水土势和易溶离子含量随深度的分布有着重要的影响,在植物根系发育带的土壤中含水量、水土势和易溶离子含量升高。

The depth to water table in the Ejina Oasis in the lower reaches of the Heihe River and along the mainstream in the lower and middle reaches is shallow, which is an important factor for maintaining the growth of vegetations in these areas. The seasonable bimodal variation in water table near Gaotai in the middle reaches is more favorable to the growth of vegetations than the seasonable unimodal variation in water table in the Ejina Oasis in the lower reaches. Similar trends of variations in soil moisture potential, water content and salt content with depth may be found in the aeration zone at the same moment. More soluble ion contents in the soils in the aeration zone at the sampling sites are relatively low with a total salt content of 〈5%. At the sampling sites in the lower reaches, SO4^2- predominates and SO4^2-, Cl^-, Na^＋ and Ca^2＋ constitute the major soluble salts in the soils of the aeration zone, while HCO3^- is the dominant ion in the sampled soils in the middle reaches. More soluble ion contents in soils have a general trend of decreasing with depth from the surface to water table. Occurrence of the root system of vegetations in soils has a significant influence On the water content, soil moisture potential and more soluble ion contents in the aeration zone, as is exemplified by the increases in water content, soil moisture potential and more soluble ion contents in soils within the root zone of some plants.